The present invention relates to silent chain, or chain with links having inverted teeth. Such chains are utilized with sprockets in automotive transmissions, transfer cases, engine timing systems, and the like. More particularly, the present invention relates to a silent chain in which the deformation of the guide link plates by a load is made substantially equal to the deformation of the inside link plates, which results in the decreased bending of the joining pins and minimizes the occurrence of fracture.
Silent chains are formed by the arrangement of link plates in lateral and longitudinal directions. The links are interlaced and joined by rocker pins. Guide links are utilized to maintain the links on the center of the sprockets when they are wound around the sprockets. Guide link plates, a, having the shape shown in FIG. 10, are typically installed in the center or at both edges of the row of link plates arranged in the lateral direction. The guide links are conventionally press fit over pins, which connect the interlaced inside or articulating links. Conventional guide plates "a" each have an inner edge facing a sprocket when wound therearound and an outer edge opposite to the inner edge, as shown in FIG. 10. The words "inner" and "outer" will hereinafter be used to define the location of the link portions with respect to the chain loop, namely, the words "inner" and "outer" respectively refer to the inner side and the outer side of the chain loop.
When load is applied to such a silent chain, a deformation moment, directed as shown by an arrow in FIG. 1, acts upon the inside or articulating link plate and causes the deformation of the link plate, as shown by the broken line in the same figure. This deformation is due to the presence of the crotch portion located between the two inverted teeth.
However, because a conventional guide link plate, a, as shown in FIG. 10, does not have inverted teeth or a crotch, its deformation is small compared with that of the inside link plate, and the difference in the deformation between the link plate and guide link plate can easily lead to the bending of the rocker pin and its fracture.
One of the prior art methods developed to overcome the drawback described above is disclosed in Examined Japan Patent Application 51-1815. According to this method, a guide link plate is used, which is provided with a depression or indentation at its outer edge (an edge opposite to the side at which the crotch or depression of the inside link plate is formed). This approach equalizes the deformations in the direction of the chain pitch line, but results in the twisting of the rocker pin because the deformation moments acting upon the link plate and guide link plate are directed in opposite directions. This twisting of the rocker pin can easily result in its fracture.
According to another conventional method disclosed in Examined Japan Patent Application 1-55821, one link plate is installed at the inner side of the outer guide link plate to prevent the contact damage of the rocker pin. This method, however, fails to completely solve the basic problem because it does not eliminate the difference in deformations of the guide link plate and link plate. Moreover, the addition of the link plate increases the width and weight of the chain for the same nominal transmission load.
Other prior art patents have addressed the unequalized loading of the pins in a silent chain. For example, U.S. Pat. No. 4,915,675 to Avramidis, which is incorporated herein by reference, teaches that loading across the pins should be equalized by matching the elastic deformation of the guide links to the elastic deformation of the inside links. U.S. Pat. No. 4,915,675 discloses, in various embodiments, the use of kidney shaped guide links as well as guide links of different thickness to match the stiffness or elasticity of the two outside guide links with the plurality of inside links in the adjacent rows. In accordance with the lacing pattern, the guide link is constructed to match the loading across the pins and the two guide links on a pin elastically deform substantially equally with the plurality of inside links.
Similarly, U.S. Pat. No. 2,602,344 to Bremer teaches that the loading across the pins should be equalized. U.S. Pat. No. 2,602,344 teaches a keyhole shape or removal of material to form a crotch in the guide link to achieve an equalized load through matching of the load deflection of the guide links and articulating links.
U.S. Pat. No. 5,176,586 to Sugimoto utilizes the same concepts taught in U.S. Pat. Nos. 4,915,675 and 2,602,344 to provide an equal load distribution. U.S. Pat. No. 5,176,586 provides a guide link with a window hole in the central part of the guide link. The window hole provides a guide link with a stiffness that will equalize the load across the pin in the same manner as taught in the other prior art patents. The present invention utilizes these same concepts to provide an equal load distribution through a guide link with a specially shaped crotch or central window hole.